Despite the susceptibility of the elderly to drug-related problems, few studies have focused on drug-related complications leading to hospitalization in this population. Although some clinical and physiological factors that contribute to drug-related problems in the elderly have been investigated, factors that are amenable to preventive measures have not been well defined. The proposed retrospective cohort study will characterize and quantify drug-related adverse events associated with hospital admissions in the elderly and will examine two potentially preventable causes of drug related admissions: inappropriate physician prescribing practices and poor patient compliance with drug regimen. The study population will be drawn from all patients 65 years of age and over who have nonscheduled admissions to a community hospital. In Phase 1 of the study, a protocol for the identification and characterization of drug-related problems will be developed and validated. The protocol will: 1) list the clinical manifestations produced by the drug-related problem, 2) assess the severity of the drug-related problem, 3) determine the specific nature of the drug-related problem, 4) rate the preventability of the problem, 5) determine the degree to which the drug-related problem contributed to the hospital admission, and 6) establish the level of certainty of a causal relationship between the identified drug-related problem and the hospital admission. In Phase 2 of the study, the protocol will be applied to identify hospital admissions attributable, at least in part, to drug-related adverse events. Physician prescribing practices and patient compliance with drug regimen will be evaluated for patients with drug-related and non-drug-related admissions. The relative contributions of sociodemographic, clinical and drug regimen factors to the occurrence of drug-related problems will also be determined. Physician prescribing practices will be assessed by a review panel of physicians and pharmacists using a standardized procedure; patient compliance will be assessed by self-report. The study will test the following hypotheses: that inappropriate physician prescribing practices substantially contribute to the number of drug-related problems leading to hospital admission; that a significant proportion of drug-related admissions result from patient noncompliance with drug regimen; and that there is a relationship between physician prescribing practices and patient compliance. Identifying the specific nature of problems with patient compliance and physician prescribing practices are critical first steps for developing effective interventions designed to reduce drug-related problems leading to hospitalizations among geriatric populations.